Fuel cell systems generally include a fuel cell stack that produces electrical energy based on a reaction between a hydrogen feed gas and an oxidant feed gas (e.g., pure oxygen or oxygen-containing air). The hydrogen-based feed gas and oxidant feed gas are supplied to the fuel cell stack at appropriate operating conditions (i.e., temperature and pressure) for reacting therein.
In a typical fuel cell powered vehicle, the storage of liquid hydrogen requires complex, multi-layer, vacuum super isolated (insulated) tanks due to the low storage temperature of liquid hydrogen (approximately 20 degrees Kelvin or −423.67 Fahrenheit). Generally, these insulated tanks will contain an amount of gaseous hydrogen, some of which must be removed prior to or during filling of these tanks. Typically, not all of the gaseous hydrogen will be removed during filling, as some gaseous hydrogen is desirable within the tank. Thus, a certain level of liquid hydrogen in the tank should not be exceeded. A typical method of overfill protection is to use a level indicator inside the tank to measure the actual filling status. When the desired level is reached, a control system commands a valve to close, so the tank filling process ends. This system depends on a properly working level indicator and software. It is desired, however, to have a second overfilling protection system that is independent from the level indicator. Accordingly, a need exists for a system able to prevent overfilling of the liquid hydrogen tank to ensure that a desired amount of gaseous hydrogen remains in the tank.